Hmm, that sounds pretty strange. You should definitely take a HPT... And you should probably go to the doctors too.
Knowing that you are or aren't pregnant can make a big difference in whether your symptoms are a problem or not.
Heartburn and nausea can be
pregnancy symptoms, (usually starting before three months along but it's different for everyone,) but if you're pregnant you should also be gaining weight.
All of the things you mentioned, even your period going away, can be caused by stress.
So yeah, take a HPT, and to to the doctors.
Let us know how it works out, ok?